We have observed a pyrrole pigment in the bile, meconium and small intestines of newborn monkeys and man. These observations suggest that there is an enterohepatic circulation of heme protein derivatives in the neonatal period. The enterohepatic circulation of these compounds will be investigated. The chemical structure and metabolism of bile pigments found in the gallbladder, meconium, intestinal wall, portal vein, intestinal lymphatics, urine and aminiotic fluid will be studied. These pigments will be studied by spectroscopic methods, thin layer high pressure liquid chromatography, and by studies with radioactive isotopes. Attempts will be made to identify chemically the structure of these compounds.